Target-related coupling in bimanual reaching movements

While bimanual interference effects can be observed when symbolic cues indicate the parameter values of simultaneous reaching movements, these effects disappear under conditions in which the target locations of two movements are cued directly. The present study investigates the generalizability of these target-location cuing benefits to conditions in which symbolic cues are used to indicate target locations (i.e., the end points of bimanual movements). Participants were asked to move to two of four possible target locations, being located either at the same and different distances (Experiment 1), or in the same and different directions (Experiment 2). Circles and crosses served as symbolic target-location cues and were arranged in a symmetric or non-symmetric fashion over the four target locations. Each trial was preceded by a variable precuing interval. Results revealed faster initiation times for equivalent as compared to non-equivalent target locations (same vs. different cues). Moreover, the time course of prepartion suggests that this effect is in fact due to target-equivalence and not to cue-similarity. Bimanual interference relative to movement parameter values was not observed. These findings suggest that cuing target locations can dominate potential intermanual interference effects during the concurrent programming of different movement parameter values.     

The influence of movement cues on intermanual interactions

In two experiments, we studied intermanual interactions in bimanual reversal movements and bimanual aiming movements. Targets were presented on a monitor or directly on the table on which the movements were produced. Amplitudes for each hand were cued symbolically or spatially either in advance of an imperative signal or simultaneous with it. In contrast to findings of Diedrichsen et al. (Psychological Science, 12, 493–498, 2001), reaction times for different-amplitude movements were longer than for same-amplitude movements both for symbolic and spatial cues presented on the monitor and directly on the table. However, with symbolic cues the effect of the relation between target amplitudes was considerably stronger than with spatial cues, no matter where the cues were presented. Intermanual correlations of amplitudes, movement times, and reaction times were smaller with different than with same target amplitudes, and this modulation was more pronounced when targets and cues were presented on the monitor than when they were presented on the table. The findings are taken to suggest that the basic reaction-time disadvantage of different-amplitude movements results from interference between concurrent processes of amplitude specification. Additional factors like interference between concurrent processes of mapping cues on movement characteristics may add strongly to it.     

Target selection during bimanual reaching to direct cues is unaffected by the perceptual similarity of the targets

Investigations of bimanual movements have shed considerable insight on the constraints underlying our ability to perform coordinated actions. One prominent limitation is evident when people are required to produce reaching movements in which the two trajectories are of different amplitudes and/or directions. This effect, however, is only obtained when the movements are cued symbolically (e.g., letters indicate target locations); these planning costs are absent when the target locations are directly cued (J. Diedrichsen, E. Hazeltine, S. Kennerley, & R. B. Ivry, 2001). The present experiments test whether the absence of planning costs under the latter condition is due to the perceptual similarity of the direct cues. The results demonstrate that measures of response planning and execution do not depend on the perceptual similarity of the direct cues. Limitations in our ability to perform distinct actions with the two hands appear to reflect interactions related to response selection involving the translation of symbolic cues into their associated movements rather than arise from interactions associated with perception, motor programming, and motor execution.     

Bimanual cross-talk during reaching movements is primarily related to response selection,not the specification of motor parameters

Simultaneous reaching movements made with the two hands can show a considerable increase in reaction time (RT) when they differ in terms of direction or extent, compared to when the movements involve the same direction and extent. This cost has been attributed to cross-talk in the specification of the motor parameters for the two hands. However, a recent study [Diedrichsen, Hazeltine, Kennerley, & Ivry, (2001). Psychological Science, 12, 493-498] indicates that when reaching movements are cued by the onset of the target endpoint, no compatibility effects are observed. To determine why directly cued movements are immune from interference, we varied the stimulus onset asynchrony for the two movements and used different combinations of directly cued and symbolically cued movements. In two experiments, compatibility effects were only observed when both movements were symbolically cued. No difference was found between compatible and incompatible movements when both movements were directly cued or when one was directly cued and the other was symbolically cued. These results indicate that interference is not related to the specification of movement parameters but instead emerges from processes associated with response selection. Moreover, the data suggest that cross-talk, when present, primarily shortens the RT of the second movement on compatible trials rather than lengthening this RT on incompatible trials.     

Bimanual interference with compatible and incompatible tool transformations

The present study investigates bimanual interference in a tool-use task, in which two target locations had to be touched concurrently with two tools, one for each hand. Target locations were either in the same, or in different directions for the two hands. Furthermore, the tools implemented either a compatible or an incompatible relationship between the direction of target locations and the direction of associated bodily movements. Results indicated bimanual interference when the tools had to be moved to targets in different directions. Furthermore, this interference was much more pronounced when the tools required body movements that were spatially incompatible to the cued target locations as compared to when they were compatible. These results show that incompatible relationships between target directions and bodily movement directions can aggravate bimanual interference in tool use.     

Intermanual interactions related to movement amplitudes and endpoint locations

In almost all studies of bimanual movements with same and different amplitudes, the difference between amplitudes has been confounded with a difference between endpoint locations. The present authors varied those parameters orthogonally. In addition, they presented target locations on the surface on which the movements were produced (direct cues) and on a monitor (indirect cues). Participants' (N = 12) reaction times were longer when both amplitudes and endpoint locations differed than when they were the same. Intermanual amplitude correlations were reduced whenever 1 of the movement parameters differed for the 2 hands; only when cues were presented on the monitor was the amplitude correlation further reduced when both movement parameters were different. The results indicate that structural constraints on bimanual movements take effect on both amplitudes and endpoint locations. The relative importance of those 2 parameters is largely independent of the type of cue.     

Re-examining structural constraints on the initiation of bimanual movements: the role of starting locations, movement amplitudes, and target locations

Structural constraints affect the coordination of bimanual movements in ways that have been taken to suggest that the specification of different movement amplitudes is subject to strong intermanual interference effects. Most experiments taken to support this notion, however, confounded variations of movement amplitudes with symmetry in starting locations and variations in target location. The present experiment was designed to further investigate the relative influence of the parameters starting location, movement amplitude, and target location on bimanual movement coordination. Participants performed simultaneous reaching movements with the left and right hand from same and different starting locations to same and different target locations. On each trial, two movements could match on none, one, or all of the parameters. We assessed the influence of each parameter by comparing conditions in which only a single parameter matched between the two hands with conditions in which all parameters differed. The reaction-time data revealed some challenging results for previous studies: (1) same starting locations significantly delayed movement initiation; (2) specifying movement amplitudes had virtually no effect on movement initiation, whereas (3) selecting same target locations significantly benefited the bimanual responses. These findings cannot be taken to support the notion that amplitude specification affects the initiation of bimanual movements. Rather, they support the notion that the initial starting locations of the two hands and the selection of target locations decide about the ease with which we perform bimanual reaching movements.     

Brief bimanual force pulses: correlations between the hands in force and time.

Three experiments assessed coupling phenomena in the coordination of bimanual force pulses. Experiment 1 required symmetric force pulses (equal target forces and rise times for both hands) using the index finger of each hand. As the authors expected, on the basis of bimanual pointing movement results, this experiment revealed positive correlations between both the force rise times and the force amplitudes of the two hands. Experiments 2 and 3 included asymmetric conditions with different target force amplitudes (Experiment 2) or target rise times (Experiment 3). In Experiment 2 force amplitudes but not rise times were fully decoupled in the asymmetric condition. In the asymmetric condition of Experiment 3, however, neither rise times nor force amplitudes were fully decoupled. The results suggest a hierarchical control structure with temporal control dominating nontemporal control of bimanual force coordination.     

Bimanual interference associated with the selection of target locations

Four experiments were conducted to identify the locus of interference observed during the preparation of bimanual reaching movements. Target locations were specified by color, and the right-hand and left-hand targets could be either the same or a different color. Movements of different amplitudes (Experiment 1) or different directions (Experiment 2) to targets of the same color were initiated more quickly than symmetric movements to targets of different colors. These results indicate that costs observed during bimanual movements arise during target selection rather than during motor programming. Experiments 3 and 4 further examined the interference associated with target selection. Reaction time costs were found with unimanual movements when the target was presented among distractors associated with responses for the other hand. Interference observed during bimanual reaching appears to reflect difficulty in segregating the response rules assigned to each hand.     

Response Selection Contributes to the Preparation Cost for Bimanual Asymmetric Movements

Movement preparation of bimanual asymmetric movements takes more time than bimanual symmetric movements in choice reaction-time conditions. This bimanual asymmetric cost may be caused by increased processing demands on any stage of movement preparation. The authors tested the contributions of each stage of movement preparation to the asymmetric cost by using the additive factors method. This involved altering the stimulus contrast, response compatibility, and response complexity. These manipulations changed the processing demands on stimulus identification, response selection, and response programming, respectively. Any manipulation with a larger reaction time cost than control suggests that stage contributes to the bimanual asymmetric cost. The bimanual asymmetric cost was larger for incompatible stimuli, which supports that response selection contributes to the bimanual asymmetric cost.     

Parametric coupling and generalized decoupling revealed by concurrent and successive isometric contractions of distal muscles

In two experiments we examined the hypothesis of transient parametric coupling during the specification of peak forces of isometric contractions produced by the left and right hand. In the first experiment participants had to produce bimanual contractions with same and different target forces as rapidly as possible in response to an auditory signal; target forces were cued visually with variable cueing intervals. At short cueing intervals reaction times were longer when different peak forces had to be specified than when same peak forces were cued, and this reaction-time difference declined as the cueing interval was increased. Independent of the cueing interval intermanual correlations of peak forces, rise times, and reaction times were smaller in conditions with different peak forces than in those with same peak forces. In the second experiment imperative signals for left-hand and right-hand contractions were separated in time. Target forces for the first response were cued with variable cueing intervals, while for the second response the cues were presented simultaneously with the second imperative signal. Reaction time of the second response was longer when target forces for the two successive responses were different rather than same, and this reaction-time difference declined when the delay of the second signal was increased as well as when the cueing interval for the first response became longer. These results are consistent with the hypothesis of a transient cross-talk between concurrent processes of peak-force specifications; in addition they indicate generalization of the decoupling required to specify different peak forces concurrently to the specification of temporal response characteristics and to processes of response initiation.     

Functional coupling between the limbs during bimanual reach-to-grasp movements

While it is frequently advantageous to be able to use our hands independently, many actions demand that we use our hands co-operatively. In this paper we present two experiments that examine functional binding between the limbs during the execution of bimanual reach-to-grasp movements. The first experiment examines the effect of gaze direction on unimanual and bimanual reaches. Even when subjects' eye movements are restricted during bimanual reaches so that they may only foveate one target object, the limbs remain tightly synchronized to a common movement duration. In contrast, grip aperture is independently scaled to the size of the target for each hand. The second experiment demonstrates however, that the independent scaling of grip aperture is task dependent. If the two target objects are unified so that they appear to be part of a single object, grip apertures become more similar across the hands (i.e., grip aperture to the large target object is reduced in size while peak aperture to the small target item is increased in size). These results suggest that the coupling of the limbs can operate at a functional level.     

The control of amplitude and direction in a bimanual coordination task

Bimanual coordination requires task-specific control of the spatial and temporal characteristics of the movements of both hands. The present study focused on the spatial relationship between hand movements when their amplitude and direction were manipulated. In the experiment in question, participants were instructed to draw two lines simultaneously. These two lines were instructed to be drawn in mirror symmetric or perpendicular directions of each other while the length was instructed to be the same or different. The coordinative quality of amplitude control was compared when the task required symmetric and asymmetric bimanual spatial coordination patterns. Results showed that the amplitude accuracy decreased when different amplitudes and/or directions had to be generated simultaneously. The coordinative quality of direction was also compared when the task required symmetric and asymmetric bimanual spatial coordination patterns. Unlike amplitude, the direction accuracy was largely independent of coordination symmetry/asymmetry of direction or amplitude. The results suggest that the coordinative quality of amplitude control does not only interfere with amplitude asymmetry, but it also interferes with direction asymmetry. Moreover, in bimanual coordination amplitude control is more vulnerable to the influence of direction control demands than vice versa.     

DISSOCIATION OF SPATIAL AND TEMPORAL COUPLING IN THE BIMANUAL MOVEMENTS OF CALLOSOTOMY PATIENTS

Abstract— The neural mechanisms of limb coordination were investigated by Jesting callosotomy patients and normal control subjects on bimanual movements. Normal subjects produced deviations in the trajectories when spatial demands for the two spatial deviations, although their hands moved with normal temporal synchrony. Normal subjects but not callosotomy patients exhibited large increases in planning and execution time for movements with different spatial demands for the two hands relative to movements with identical spatial demands for the two hands. This neural dissociation indicate that spatial interference in movements results from callosal connections whereas temporal synchrony in movement onset does not rely on the corpus callosum.     

Goal congruency in bimanual object manipulation

In 3 experiments, the authors investigated the impact of action goals on the production of discrete bimanual responses. Similar to a bartender putting 2 glasses simultaneously on a shelf, participants placed 2 objects into either parallel or opposite orientations by carrying out either mirror-symmetrical or mirror-asymmetrical movements. In Experiment 1, performance was strongly affected by the congruency of the intended object orientations but was essentially unaffected by movement symmetry. Experiment 2 replicated this instrumental goal-congruency effect (and the absence of motor-symmetry effects) when actions were cued in advance. Experiment 3 revealed substantial motor-symmetry effects, provided the movements themselves became the action goal. The authors concluded that performance in bimanual choice reaction tasks is constrained by the creation and maintenance of goal codes rather than by properties inherent in the neuromuscular system that carries out these responses. These goals can relate to either body-intrinsic states or to body-extrinsic states according to the actor's current intentions.     

Age Changes in Interlimb Coupling and the Development of Bimanual Coordination

Changes in interlimb coupling, and their role in the development of bimanual coordination, were studied longitudinally in 6- to 12-month-old infants (N = 6). Infants were observed while they were reaching for simple objects of 2 different sizes. Their use of a uni-versus bimanual strategy for reaching as well as the coupling of their bimanual movements were compared; progress in bimanual coordination of complementary movements was evaluated on 8 different bimanual tasks. The bimanual tasks involved an asymmetrical cooperation between the 2 hands. Although spatiotemporal coupling of bimanual reaching movements did not decrease during the age period studied, infants around 7 months of age used their 2 hands infrequently for reaching. Occurrences of bimanual reaching were particularly low at the session preceding the first bimanual success at a bimanual task. This suggests that the temporal coincidence between greater independence of the 2 hands and progress in bimanual coordination of complementary movements acts in 2 directions: Infants may be more at ease when using their 2 hands in differentiated patterns as the hands move less in synchrony, but, in turn, they may be less likely to move their hands in synchrony as the anticipate mirror manipulations of the object less. The frequency of bimanual reaches increased toward the end of the 1st year. This might have been caused by an increase in the repertoire of bimanual asymmetrical object manipulations and by the fact that the development of bimanual coordination allows infants to manipulate objects with complementary movements even after a bimanual approach toward the object.     

Unilateral vs. bilateral coordination of circle-drawing tasks

The number of joint motions available in the upper extremity provides for multiple solutions to the coordination of a motor task. Making use of these abundant joint motions provides for task flexibility. Controlling bimanual movements poses another level of complexity because of possible tradeoffs between coordination within a limb and coordination between the limbs. We examined how flexible patterns of joint coordination were used to stabilize the hand's path when drawing a circle independently compared to a bimanual pattern. Across-trial variance of joint motions was partitioned into two components: goal-equivalent variance (GEV), representing variance of joint motions consistent with a stable hand path and non-goal-equivalent variance (NGEV) representing variance of joint motions that led to deviations of the hand's path. GEV was higher than NGEV in both unimanual and bimanual drawing, with one exception. Both GEV and NGEV, related to control of the individual hands' motion, decreased when engaged in the bimanual compared to unimanual drawing. Moreover, NGEV, leading to variability in the vectorial distance between the hands, was higher when the two hands drew circles in a bimanually asymmetric vs. symmetric pattern, consistent with reported differences in the relative phasing of the two hands. Our results suggest that the nervous system controls the individual hands' motions by separate intra-limb synergies during both unimanual and bimanual drawing, and superimposes an additional synergy to achieve stable relative motion of the two hands during bimanual drawing.     

Kinematic parameters of hand movement during a disparate bimanual movement task in children with unilateral Cerebral Palsy

Children with unilateral Cerebral Palsy (uCP) experience problems performing tasks requiring the coordinated use of both hands (bimanual coordination; BC). Additionally, some children with uCP display involuntary symmetrical activation of the opposing hand (mirrored movements). Measures, used to investigate therapy-related improvements focus on the functionality of the affected hand during unimanual or bimanual tasks. None however specifically address spatiotemporal integration of both hands. We explored the kinematics of hand movements during a bimanual task to identify parameters of BC. Thirty-seven children (aged 10.9 ± 2.6 years, 20 male) diagnosed with uCP participated. 3D kinematic motion analysis was performed during the task requiring opening of a box with their affected- (AH) or less-affected hand (LAH), and pressing a button inside with the opposite hand. Temporal and spatial components of data were extracted and related to measures of hand function and level of impairment. Total task duration was correlated with the Jebsen–Taylor Test of Hand Function in both conditions (either hand leading with the lid-opening). Spatial accuracy of the LAH when the box was opened with their AH was correlated with outcomes on the Children’s Hand Use Experience Questionnaire. Additionally, we found a subgroup of children displaying non-symmetrical movement interference associated with greater movement overlap when their affected hand opened the box. This subgroup also demonstrated decreased use of the affected hand during bimanual tasks. Further investigation of bimanual interference, which goes beyond small scaled symmetrical mirrored movements, is needed to consider its impact on bimanual task performance following early unilateral brain injury.     

Detection costs and contingent attentional capture

Peripheral cues reduce reaction times (RTs) to targets at the cued location with short cue-target SOAs (cueing benefits) but increase RTs at long SOAs (cueing costs or inhibition of return). In detection tasks, cueing costs occur at shorter SOAs and are larger compared with identification tasks. To account for effects of task, detection cost theory claims that the integration of cue and target into an object file makes it more difficult to detect the target as a new event, which is the principal task-requirement in detection tasks. The integration of cue and target is expected to increase when cue and target are similar. We provided evidence for detection cost theory in the modified spatial cueing paradigm. Two types of cues (onset, color) were paired with two types of targets (onset, color) in separate blocks of trials. In the identification task, we found cueing benefits with matching (i.e., similar) cue-target pairs (onset-onset, color-color) and no cueing effects with nonmatching cue-target pairs (onset-color, color-onset), which replicates previous work. In the detection task, cueing effects with matching cues were reduced and even turned into cueing costs for onset cues with onset targets, suggesting that cue-target integration made it more difficult to detect targets at the cued location as new events. In contrast, the results for nonmatching cue-target pairs were not affected by task. Furthermore, the pattern of false alarms in the detection task provides a measure of similarity that may explain the size of cueing benefits and costs.     

Goal congruency without stimulus congruency in bimanual coordination

Two experiments explored the role of stimulus congruency and goal congruency for the generation of object-oriented actions with two hands. Participants had to place two objects into either parallel or opposite orientations by carrying out either symmetrical or asymmetrical forearm rotations. Performance was superior when the required object orientations were identical rather than different, almost independent of the symmetry of the required arm movements. In extending previous research, goal congruency effects ensued even under conditions in which congruency of imperative response signals could not have contributed to goal congruency effects, either because only a single stimulus was used to indicate the required goals in an individual trial (Experiment 1) or such stimuli were absent at all (Experiment 2). The results thus confirm the importance of goal codes for the reconcilableness of bimanual actions, and rule out accounts in terms of stimulus-related processes.